Abstract
The olfactory pathway integrates the odor information required to generate correct behavioral responses. To address how changes of serotonin signaling in two contralaterally projecting, serotonin-immunoreactive deutocerebral neurons impacts key odorant attraction in Drosophila melanogaster, we selectively alter serotonin signaling using the serotonin transporter with mutated serotonin binding sites in these neurons and analyzed the consequence on odorant-guided food seeking. The expression of the mutated serotonin transporter selectively changed the odorant attraction in an odorant-specific manner. The shift in attraction was not influenced by more up-stream serotonergic mechanisms mediating behavioral inhibition. The expression of the mutated serotonin transporter in CSD neurons did not influence other behaviors associated with food seeking such as olfactory learning and memory or food consumption. We provide evidence that the change in the attraction by serotonin transporter function might be achieved by increased serotonin signaling and by different serotonin receptors. The 5-HT1B receptor positively regulated the attraction to low and negatively regulated the attraction to high concentrations of acetic acid. In contrast, 5-HT1A and 5-HT2A receptors negatively regulated the attraction in projection neurons to high acetic acid concentrations. These results provide insights into how serotonin signaling in two serotonergic neurons selectively regulates the behavioral response to key odorants during food seeking.
Highlights
Animals such as mammals and insects heavily rely on the olfactory system to search for and detect a suitable food source
Since the contralaterally projecting serotonin-immunoreactive deutocerebral (CSD) neurons synapse onto the mushroom body calyx (MB), a structure involved in the regulation of olfactory learning and memory, we addressed whether short-term olfactory appetitive, aversive or aversive reversal learning and memory is altered by altered serotonin signaling in the CSD neurons
Altered serotonin signaling in CSD neurons by blocking serotonin reuptake with the expression of a serotonin transporter with mutated serotonin binding sites increased the attractiveness of higher ethanol concentrations within a food odor blend [18]
Summary
Animals such as mammals and insects heavily rely on the olfactory system to search for and detect a suitable food source. The olfactory system is a powerful system for decoding odor information that is relevant for the animal’s energy demands. The relevance of odor information to the animal might be assessed by examining the behavioral response to the odor information in a choice situation. Animals might respond with approach, avoidance or indifference. A food source such as an apple emits a complex odor bouquet [1]. In addition to the fruit smell, yeast might settle on the surface, contributing its own typical smell of ethyl acetate (EtOAc) [2]. Yeast converts fruit sugar into the odorant ethanol (EtOH). Ethanol in turn is converted into acetic acid (AA) by the bacteria acetobacter spec.
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